The svn:ignore property contains a list of file patterns which certain Subversion operations will ignore. Perhaps the most commonly used special property, it works in conjunction with the global-ignores run-time configuration option (see the section called “Config”) to filter unversioned files and directories out of commands svn status , svn add , and svn import .

The rationale behind the svn:ignore property is easily explained. Subversion does not assume that every file or subdirectory in a working copy directory is intended for version control. Resources must be explicitly placed under Subversion's management using the svn add or svn import commands. As a result, there are often many resources in a working copy that are not versioned.

Now, the svn status command displays as part of its output every unversioned file or subdirectory in a working copy that is not already filtered out by the global-ignores option (or its built-in default value). This is done so that users can see if perhaps they've forgotten to add a resource to version control.

But Subversion cannot possibly guess the names of every resource that should be ignored. Also, quite often there are things that should be ignored in every working copy of a particular repository. To force every user of that repository to add patterns for those resources to their run-time configuration areas would be not just a burden, but has the potential to clash with the configuration needs of other working copies that the user has checked out.

The solution is to store ignore patterns that are unique to the resources likely to appear in a given directory with the directory itself. Common examples of unversioned resources that are basically unique to a directory, yet likely to appear there, include output from program compilations. Or—to use an example more appropriate to this book—the HTML, PDF, or PostScript files generated as the result of a conversion of some source DocBook XML files to a more legible output format.

$ svn propset svn:ignore -F .cvsignore .
property 'svn:ignore' set on '.'
$

For this purpose, the svn:ignore property is the solution. Its value is a multi-line collection of file patterns, one pattern per line. The property is set on the directory in which you wish the patterns to be applied. ^[34] For example, say you have the following output from svn status :

$ svn status calc
 M     calc/button.c
?      calc/calculator
?      calc/data.c
?      calc/debug_log
?      calc/debug_log.1
?      calc/debug_log.2.gz
?      calc/debug_log.3.gz

In this example, you have made some property modifications to button.c, but in your working copy you also have some unversioned files: the latest calculator program that you've compiled from your source code, a source file named data.c, and a set of debugging output log files. Now, you know that your build system always results in the calculator program being generated. ^[35] And you know that your test suite always leaves those debugging log files lying around. These facts are true for all working copies, not just your own. And you know that you aren't interested in seeing those things every time you run svn status . So you use svn propedit svn:ignore calc to add some ignore patterns to the calc directory. For example, you might add this as the new value of the svn:ignore property:

calculator
debug_log*

After you've added this property, you will now have a local property modification on the calc directory. But notice what else is different about your svn status output:

$ svn status
 M     calc
 M     calc/button.c
?      calc/data.c

Now, all the cruft is missing from the output! Of course, those files are still in your working copy. Subversion is simply not reminding you that they are present and unversioned. And now with all the trivial noise removed from the display, you are left with more interesting items—such as that source code file that you probably forgot to add to version control.

If you want to see the ignored files, you can pass the --no-ignore option to Subversion:

$ svn status --no-ignore
 M     calc/button.c
I      calc/calculator
?      calc/data.c
I      calc/debug_log
I      calc/debug_log.1
I      calc/debug_log.2.gz
I      calc/debug_log.3.gz

The list of patterns to ignore is also used by svn add and svn import . Both of these operations involve asking Subversion to begin managing some set of files and directories. Rather than force the user to pick and choose which files in a tree she wishes to start versioning, Subversion uses the ignore patterns to determine which files should not be swept into the version control system as part of a larger recursive addition or import operation.